Erectile dysfunction (ED) affects ~ 50% of men aged 40 to 70 and has a high impact on men's health and quality of life. Current treatments are ineffective in the difficult to treat prostatectomy (16-82%) and diabetic (56-59%) patients due to injury to the cavernous nerve (CN), which provides innervation to the penis. With denervation the critical smooth muscle (SM) undergoes apoptosis and the penis becomes fibrotic, with increased collagen abundance and a change in subtypes, thus altering the architecture of the corpora cavernosa. This application is significant because we propose a novel integrative approach that targets the 3 main morphological changes that underlie ED, which are CN degeneration, SM apoptosis, and penile fibrosis. We've shown that sonic hedgehog (SHH) is a critical regulator of SM apoptosis in the penis and of CN regeneration. SHH pathway is of high interest as a candidate ED therapy because SHH regulates a critical nexus of pathways required to maintain erectile function. Our data in prostatectomy and diabetic patients shows altered morphology and decreased SHH protein in high fidelity to our rat ED model. In the rat SHH inhibition causes demyelination and axonal degeneration of CN fibers and CN crush decreases SHH protein 70% in the CN. SHH inhibition in the penis causes SM apoptosis and ED while CN crush decreases penile SHH. We show reversible penile remodeling with reestablishment of SHH signaling using two innovative peptide amphiphile (PA) delivery prototypes. In a crush model, SHH treatment of the CN (PA1) and of the penis (PA2) accelerates regeneration, improves erectile function >60%, suppresses apoptosis and preserves penile SM 56%. We will extend our observations to improve effectiveness of SHH delivery for maximal apoptosis suppression and CN regeneration in preparation for clinical translation (Aim 1), and design PAs that bind to SHH to fine tune release kinetics and duration in vivo in the penis (Aim 2). SHH PAs will be examined in an aged prostatectomy model that better simulates ED patient conditions (Aim 3). SHH PA is highly translatable for treatment of prostatectomy and diabetic patients by substituting human SHH protein for rat. SM apoptosis (2-7 days) occurs before increased collagen (7-14 days) in prostatectomy patients. We propose the innovative hypothesis that suppressing SM apoptosis can prevent the fibrotic response (Aim 4). Increased collagen is common in ED patients following prostatectomy. We show collagen abundance is responsive to SHH signaling (SHH inhibition increases collagen/SHH treatment decreases collagen), by an unknown mechanism. Microarray of corpora cavernosa from ED patients shows increased Gremlin 1, a BMP4 antagonist. SHH is a regulator of Gremlin in limb bud, Gremlin regulates fibrosis in lung, and BMP4 is inversely responsive to SHH during development. We hypothesize that reduced SHH that occurs in the penis with CN injury, up-regulates BMP4 leading to fibrosis (Aim 4). Understanding where intervention in the penile remodeling process will be effective to prevent ED is critical for development of novel therapies.